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Take a look at the two images above. Which scares you more? Most people would say they’re more afraid of the snake, despite cars killing over 30,000 Americans per year and snakes killing an average of 5. Why are we so afraid of snakes, spiders, and bats, but not SUVs? The answer lies in our evolutionary history.

There are some things that we learn to fear. If someone is badly bitten by a guinea pig, they may come to be uncomfortable around guinea pigs. Other fears appear to be written into our DNA. Babies will often respond with fear to a toy snake, even when they’ve never had a bad experience with a real one. Once, scientists thought these sorts of inherent fears evolved during our time spent on the African plains in the Stone Age. However, it seems that the root of our fears goes back even further than that.

There are some fears that are shared by our animal relatives. Chimpanzee and monkey babies respond in the same way as human infants to rubber snakes, acting fearful and startled to see one nearby. It is very likely that early primates had an ingrained fear of snakes that they passed down to their evolutionary descendants.

Image by Pascal Reusch

Fear of heights is another common phobia. How recently did this evolve? In the 1960s, scientists conducted an experiment to test the commonality of this fear. They gave infants and baby goats the opportunity to walk onto a transparent surface, simulating walking over a cliff.

Neither goat nor human were too keen on walking onto the surface and putting gravity to the test. Evolutionarily speaking, having a fear of heights is useful for most land-dwelling animals. It’s a bad idea to hang around sharp precipices if you can’t fly.

Animals inherently fear that which has the greatest likelihood of harming them. Baby rhesus monkeys are afraid of toy crocodiles, but not toy rabbits. Crocodiles are a frequent predator for these monkeys, and rabbits are not.

In the modern day, it's clear that evolution hasn’t had time to catch up with our fear programming. Cars and guns kill multitudes of people each year, but babies and many adults have no fear of either of them. Many people would rather hold a loaded gun than a harmless pet snake. This lack of evolutionary preparedness has led to tragedy. At least 265 children in the United States accidentally shot themselves or others with guns in 2015. Would that number be lower if humans evolved an inherent fear of guns? Would those same children be so cavalier about picking up a spider or a snake?

With the fast pace of our societal and technological advancement, it isn't clear when (or if) our inherent fears will properly match our dangers again. Until that happens, we just have to do our best to learn what will hurt us and take care as necessary, especially protecting the children who are too young to know that cars can mean death.

Our Most Human Fears

There are some fears that appear uniquely human. These are the most interesting of fears, the ones that we evolved to help us cope with our specifically human problems. One of these fear responses is fainting at the sight of blood. It doesn’t seem very adaptive at first glance. If we faint when we see blood, won’t that give whatever is attacking the chance to kill us? It is such a common response that scientists have long puzzled over its meaning, though now they have some ideas.

100,000 years ago in the Paleolithic age, fainting at the sight of blood may have been an adaptation for de-escalating conflict between warring human tribes. If you faint in the midst of human-on-human violence, you are less likely to attract attention or offense. An aggressor may even decide not to kill you if they see you are no longer a threat.

We had Madagascar hissing cockroaches in the office for the first six months or so after I was hired. Even just looking at pictures of cockroaches makes me a bit queasy. Image by Ltshears

Fear of vermin is an even more recent human adaptation. As societies grew more permanent they also grew denser. Vermin found ample breeding grounds in our packed cities with their food stores and garbage. Rats, mice, and insects can all spread disease. We are less likely to interact with and become infected by these animals if we fear them. Being afraid of vermin also gives people incentive to avoid potentially tainted food or living spaces. I personally have a moderate fear of cockroaches, despite never having been harmed by one. Thanks to evolution, I am compelled to live a much cleaner life than I might otherwise.

The Fear-Seekers

This is me going skydiving a couple years ago. It was one of the most fun things I've ever done!

There are many different things that we come pre-programmed to fear, so why are there people that watch horror movies, go skydiving, or go to Vegas and have snakes draped around their shoulders? Evolution gave us many of our fears, but it also gave us the tools to work around them, and even seek them out.

Humans have been successful as a species partially because of our ability to face and conquer fear. Our drive to take risks led us to spread across the globe, settling in even the harshest of conditions. Hunting large and dangerous animals is a scary prospect, but our willingness to do so provided us with excellent protein sources. People who explored new and frightening areas found new resources and places to live. We have even taken some of our most intimidating predators, wolves, and domesticated them to serve our benefit.

Our fears are part of a delicate balance, keeping us safe but also driving us to succeed. Fear serves an evolutionary purpose, and sometimes facing it does too.